抜粋：
READ_BACKUP: Setting this option to 1 has the same effect as though ndb_read_backup were enabled; enables reading from any replica.
Setting this option to 1 automatically sets FRAGMENT_COUNT_TYPE to ONE_PER_LDM_PER_NODE_GROUP (see next item).
Starting with MySQL Cluster NDB 7.5.3, you can set READ_BACKUP for an existing table online,
using an ALTER TABLE statement similar to one of those shown here:

[root@study01 bin]# pwd
/usr/local/mysql/bin
[root@study01 bin]#./mysqlslap
--no-defaults --auto-generate-sql --auto-generate-sql-guid-primary --engine=myisam
--number-int-cols=3 --number-char-cols=5 --concurrency=3 --auto-generate-sql-write-number=100
--auto-generate-sql-execute-number=1000 --auto-generate-sql-load-type=mixed -u root -p
Enter password:
Benchmark
Running for engine myisam
Average number of seconds to run all queries: 0.813 seconds
Minimum number of seconds to run all queries: 0.813 seconds
Maximum number of seconds to run all queries: 0.813 seconds
Number of clients running queries: 3
Average number of queries per client: 1000
[root@study01 bin]#./mysqlslap
--no-defaults --auto-generate-sql --auto-generate-sql-guid-primary --engine=myisam
--number-int-cols=3 --number-char-cols=5 --concurrency=5 --auto-generate-sql-write-number=100
--auto-generate-sql-execute-number=1000 --auto-generate-sql-load-type=mixed -u root -p
Enter password:
Benchmark
Running for engine myisam
Average number of seconds to run all queries: 1.448 seconds
Minimum number of seconds to run all queries: 1.448 seconds
Maximum number of seconds to run all queries: 1.448 seconds
Number of clients running queries: 5
Average number of queries per client: 1000
[root@study01 bin]#